| 摘要 |
PURPOSE:To obtain a Nyquist filter where a characteristic approximated to the Nyquist characteristic is obtained easily and inexpensively by using a Butterworth filter and setting the cut-off frequency so as to minimize the maximum inter-code interference. CONSTITUTION:As an evaluation means of the inter-code interference, the ratio of the amplitude level STL at a sampling time point (t/T=-1) of a signal while taking the right end of a main lobe, i.e., the 1st cross point as a reference point to the total sum of amplitude levels LEVi at each point of a period t=-2T, 2T, 3T ... is obtained so as to evaluate the change in the evaluated value of the cut-off frequency of the filter used as the Nyquist filter and the inter-code interference when the filter order is used as a parameter. That is, the inter-code interference EV is expressed in equation. Thus, in setting the cut-off frequency of the Butterworth low-pass filter having the desired order to a point minimizing the EV, the filter minimizing the inter-code interference is realized.
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